1. Field of the Invention
The present invention relates to a hard carbon film-coated substrate which has a hard carbon film formed on a substrate surface and to a method for fabricating the hard carbon film-coated substrate. The present invention further relates to a method for providing a hard carbon film on a substrate, more particularly to a method for providing a protective film such as on inner and outer blades of an electric shaver, magneto-optical disks, thin film magnetic heads and surface acoustic wave (SAW) devices; an antireflection film for lithography; a protective film on sliding surfaces of compressors; or a hard carbon film such as on constituent layers of solar batteries, decorative articles and optical parts.
2. Description of Related Art
It has been conventionally known that the formation of a diamond-like carbon film directly on a substrate results in poor adhesion between the diamond-like carbon film and the substrate. In order to overcome such a disadvantage, proposals have been made which interpose a Si interlayer between the diamond-like carbon film and the substrate (see, for example, Japanese Patent Laying-Open Nos. 2-182880(1990), 3-115572(1991) and 1-138611(1989)).
Japanese Patent Laying-Open Nos. 7-41386(1995) and 7-316818(1995) disclose that the adhesion between a hard carbon film and a substrate can be improved by providing an interlayer of Si, Ru or Ge therebetween even when the substrate is made of a metal or an alloy principally formed of Ni or Al, suitably used such as for an electric shaver blade, or of a stainless steel.
The above-described prior art interlayer is effective in improving adhesion and peel resistance between the substrate and the hard carbon film, e.g. the diamond-like carbon film if interposed therebetween. However, considering the technological abundance in the field and applicability to various technological situations, there still remains a need for the other type of interlayer which is also capable of improving the adhesion and peel resistance between the substrate and the hard carbon film.
The above-described conventional interlayers have been formed by vapor phase epitaxial methods such as a sputtering method and a plasma CVD method. This requires that the thickness of the interlayer be made greater, or alternatively, the substrate position be changed during the interlayer formation if the substrate has a complicated three-dimensional configuration.
It is an object of the present invention to provide a hard carbon film-coated substrate which exhibits improved adhesion and peel resistance between a hard carbon film and a substrate, and a method for providing the hard carbon film-coated substrate.
It is another object of the present invention to provide a method for providing a hard carbon film on a substrate whereby an interlayer can be uniformly formed even on a substrate having complicated three-dimensional configurations and a satisfactory adhesion can be imparted between the hard carbon film and the substrate.
The hard carbon film-coated substrate in accordance with a first aspect of the present invention includes a substrate, a hard carbon film and an interlayer formed between the substrate and the hard carbon film. The interlayer is principally comprised of at least one selected from the group consisting of Al, Cr, Sn, Co and B, oxides, nitrides and carbides thereof.
Any method such as sputtering can be employed to form the interlayer in accordance with the first aspect of the present invention. In the event that the sputtering method is employed, it is preferred to form the interlayer while applying a radio frequency voltage to a substrate so that a self-bias voltage is produced across the substrate. Preferably, the self-bias voltage produced in the substrate is controlled not to exceed xe2x88x9220 V to assure the enhanced adhesion of the hard carbon film to the substrate.
The interlayer in accordance with the first aspect of the present invention may be formed using other physical deposition or chemical vapor phase epitaxial methods. Plating may be employed to form a metallic interlayer, for example.
The term xe2x80x9chard carbon filmxe2x80x9d as used in the first aspect of the present invention is intended to include an amorphous diamond-like carbon film, a diamond-like carbon film having amorphous and crystalline portions, and a crystalline diamond-like carbon film.
A method of forming the hard carbon film in the first aspect of the present invention is not particularly limited. The hard carbon film can be formed such as by a CVD method, e.g. a plasma CVD method. Analogously to the interlayer formation, it is preferred to form the hard carbon film while applying a radio frequency voltage to a substrate so that a self-bias voltage is produced across the substrate. Preferably, the self-bias voltage produced in the substrate is controlled not to exceed xe2x88x9220 V. In the plasma CVD method, an electron cyclotron resonance (ECR) plasma CVD apparatus can be employed as a means for generating a plasma, for example. The use of such an apparatus increases a plasma density and enables a high-quality hard carbon film to be formed at low temperatures.
The hard carbon film-coated film in accordance with the first aspect of the present invention is applicable to inner and outer blades of an electric shaver, for example. Those inner and outer electric shaver blades are typically formed of a metal or an alloy principally comprised of Ni or Al, or of a stainless steel. Accordingly, a substrate formed of these materials can be employed as a substrate in the first aspect of the present invention.
The substrate is not limited to the inner and outer blades of an electric shaver, but is also applicable to magneto-optical disks, thin film magnetic heads and surface acoustic wave (SAW) devices. The hard carbon film may be provided thereon to serve as a protective film therefor. Also, the hard carbon film may be provided to serve as an antireflection film which can be used during exposure in a lithography method. Furthermore, the hard carbon film may be provided to serve as a protective film for sliding parts of a compressor such as a rotary compressor, as a solar cell protective film layer, as an optical part, or as a part of decorative articles.
The material types of the substrate in accordance with the first aspect of the present invention include cast irons such as Moxe2x80x94Nixe2x80x94Cr cast irons, steel such as high-speed tool steel, stainless steel such as SUS 304, ferrous alloys, non-ferrous metallic materials, ceramics, noble metals, and carbons. The non-ferrous metallic materials and ceramics include a single, alloy or sintered form of Ti, Al, Zr, Si, W, Mo, In, Ta, Fe, Ni, Co, Mn, Cr or Zn; and oxides, nitrides and carbides thereof. The noble metals include Au, Ag, Pt, Ru and Pd. The carbons include aluminum-impregnated carbons.
A method for providing a hard carbon film on a substrate, in accordance with the second aspect of the present invention, includes the steps of forming an interlayer on the substrate by plating and forming the hard carbon film on the interlayer.
In accordance with a narrower, second aspect of the present invention, a method includes the steps of deposition-forming a substrate on a mold through electroforming, forming an interlayer on the substrate by plating, and forming a hard carbon film on the interlayer.
In the step of forming the interlayer by plating, the interlayer can be formed while the substrate is held on the mold. This eliminates the necessity of disengaging the substrate from the mold to thereby increase the productivity of the resulting hard carbon film-coated articles.
The hard carbon film in accordance with the second aspect of the present invention includes an amorphous diamond-like carbon film and a diamond-like carbon film containing crystallites. It further includes a crystalline diamond-like carbon film.
In the second aspect of the present invention, a method of forming the hard carbon film is not particularly limited. The hard carbon film can be formed such as by a CVD method. A plasma CVD method can be employed, for example, to form the hard carbon film while applying a radio frequency voltage to a substrate so that a self-bias voltage is produced across the substrate. In such an event, it is preferred that the self-bias voltage produced in the substrate is controlled not to exceed xe2x88x9220 V. In the plasma CVD method, an electron cyclotron resonance (ECR) plasma CVD apparatus can be employed as a means for generating a plasma, for example. The use of such an apparatus increases a plasma density and enables a high-quality hard carbon film to be formed at low temperatures.
In the step of forming the interlayer by plating, generally-employed plating techniques may be adopted which include electroplating and electroless plating. When the electroplating is employed to form the interlayer, it is generally required that at least a surface of the substrate be electrically conductive.
In accordance with the second aspect of the present invention, the interlayer is formed by plating. This enables the interlayer to be formed to a uniform thickness even on the substrate having complicated three-dimensional configurations. Accordingly, the interlayer can be uniformly formed even on substrate edge portions which have been difficult to be covered through thin film formation by conventional vapor phase methods. As a consequence, the adhesion of the hard carbon film to the substrate is enhanced. Also, such a uniform formation of the interlayer permits an average thickness of the interlayer to be controlled smaller than that of the interlayer formed by conventional vapor phase methods.
The thickness of the interlayer in accordance with the second aspect of the invention is not particularly specified, but is preferably in the range of 50-5000 xc3x85, more preferably in the range of 100-3000 xc3x85.
In accordance with the second aspect of the present invention, the interlayer can be uniformly formed even on a substrate having the above-described complicated three-dimensional configurations. Accordingly, the present method is advantageously applicable to a substrate having complicated three-dimensional configurations, e.g. inner and outer blades of an electric shaver. The electric shaver blades are generally formed of a metal or an alloy principally comprised of Ni or Al, or stainless steel. Thus, the second aspect of the present invention is advantageously applicable to those substrates.
The substrate is not limited to the inner and outer blades of an electric shaver, but is also applicable to magneto-optical disks, thin film magnetic heads and surface acoustic wave (SAW) devices. The hard carbon film may be provided thereon to serve as a protective film therefor. Also, the hard carbon film may be provided to serve as an antireflection film which can be used during exposure in a lithography method. Furthermore, the hard carbon film may be provided to serve as a protective film for sliding parts of a compressor such as a rotary compressor, as a solar cell protective film layer, as an optical part, or as a part of decorative articles.
The material types of the substrate in accordance with the second aspect of the present invention include cast irons such as Moxe2x80x94Nixe2x80x94Cr cast irons, steel such as high-speed tool steel, stainless steel such as SUS 304, ferrous alloys, non-ferrous metallic materials, ceramics, noble metals, and carbons. The non-ferrous metallic materials and ceramics include a single, alloy or sintered form of Ti, Al, Zr, Si, W, Mo, In, Ta, Fe, Ni, Co, Mn, Cr or Zn; and oxides, nitrides and carbides thereof. The noble metals include Au, Ag, Pt, Ru and Pd. The carbons include aluminum-impregnated carbons.
Any interlayer material which can be formed by plating and enhance the adhesion between the substrate and the hard carbon film may be utilized. The specific examples of the interlayer materials include metals such as Ru, Cr, Sn and Co, and alloys principally comprised thereof.
Also, the interlayer in the second aspect of the present invention may be formed by composite plating which disperses fine particles such as of ceramics throughout a resulting metallic film. Such composite plating can be accomplished by conventionally known techniques. The metallic film containing fine particles in a dispersed form can be generally produced by plating in a plating bath containing dispersions of fine particles.
Examples of the fine particles dispersed in the composite metallic film include oxides, nitrides and carbides of Al, Ru, Ti, Cr, Sn, Co, Si, B or Zr. The content of fine particles dispersed in the metallic film is preferably in the range of 0.1-30 volume %, more preferably in the range of 1-10 volume %. The preferred particle size of the fine particles is not greater than 1 xcexcm.
In the event that the composite metallic film is formed as the interlayer in accordance with the second aspect of the present invention, the fine particles dispersed in the metallic film are effective in enhancing the adhesion to the overlying hard carbon film. Accordingly, the material which constitutes a matrix in the metallic film can be selected from a wider range of materials than the above-described materials for the metallic film. For example, the adhesion of the hard carbon film to a Ni substrate can be improved by plating on the Ni substrate the material identical to that of the substrate, i.e. Ni, to form a Ni film in which the fine particles are dispersed.